The present invention relates to a process for converting filtration residues of crude sodium obtained by fusion electrolysis methods and of viscous-to-hard consistency at temperatures above the sodium melting point into a material of thin consistency.
The sodium produced by fusion electrolysis at about 600.degree. C., namely the so-called crude sodium, contains about 2% contamination. In addition to slight amounts of entrained crucible melt (BaCl.sub.2, CaCl.sub.2, NaCl) and oxides, hydroxides as well as carbonates of sodium and calcium, metallic calcium is primarily present, which during cooling to a temperature of about 120.degree. C. will extensively segregate and which together with the other impurities will be filtered and separated out by a steel wire mesh filter at that temperature.
The calcium content of the sodium purified in this manner to obtain the so-called standard grade of sodium as a rule is 300-600 ppm, whereas the oxide and chloride content each will be less than 10 ppm. The filter residue, the so-called filter sludge, on the other hand contains a calcium content of about 15-21% by weight, on the average about 17% by weight.
As the impurities of the above-mentioned filter residues increase, the filter sludge becomes viscous-to-hard at temperatures about the sodium melting point and therefore presents handling problems. Illustratively, the sludge to be removed from the filter equipment had to be moved to a conveyor screw mounted at the bottom of this filter equipment, and heretofore this has been possible only by employing substantial manual effort. No pumping, pressure conveyor or suction equipment could be used to convey the residue for purposes of processing; instead any shipping of such materials had to be carried out in containers filled and emptied manually by shovel.